Lightweight rechargeable batteries are used in many electrically powered devices, for example, cellular phones, pagers, computers, and power tools. One popular rechargeable battery is the lithium ion battery. Lithium ion batteries that are commercially available today use a liquid electrolyte. This electrolyte is organically based. Consequently, lithium ion batteries must be sealed in rigid `cans` to prevent the leakage of the electrolyte. There is a desire to eliminate the rigid can and move toward flexible, light-weight, leak-tight packaging, e.g., metallized plastic or foil bags.
One method suggested for eliminating the can is the use of solid electrolytes. See U.S. Pat. Nos. 5,296,318; 5,437,692; 5,460,904; 5,639,573; 5,681,357; and 5,688,293. Solid electrolytes include two types, a solid electrolyte and a gel electrolyte. Of these two types, the gel electrolyte is preferred because of its greater conductivity. Gel electrolytes, however, are deficient because they cannot easily provide the structural integrity necessary to separate the positive and negative electrodes,for example, during manufacture, and to provide the shutdown capability necessary to safely handle the electrodes, for example, during an overcharge condition.
In U.S. Pat. Nos. 5,639,573; 5,681,357; and 5,688,293, it is proposed that a microporous membrane (or inert layer), in combination with an absorbing or gel-forming polymer, be used as a separator system. After the electrolyte is injected into the separator system, the gel-forming polymer is cured to form the gelled electrolyte around the microporous membrane whereby the structural intregity of the gel electrolyte is enhanced by the inclusion of a microporous membrane.
In the manufacture of the foregoing battery, the occurrence of delamination or separation of the absorbing or gel-forming layer from the inert layer is detrimental. Accordingly, there is a need for a new separator which improves the adherence of the microporous membrane to the gel-forming polymer and thereby reduces delamination or separation of these two components during manufacturing.